β-Amylase can attack to both 2-chloro-4-nitrophenyl-α-D-maltotrioside (G3-CNP) and p-nitrophenyl-β-D-maltopentaoside (G5-PNP), respectively forming G1-CNP and G1-PNP. These compounds can be further cleaved to CNP or PNP by the action of yeast α-glucosidase. However, the nitrophenyl- G1 derivatives were not formed from G4-PNP or G6-PNP by the enzyme, although β-amylase could be weakly detected in a Phadebas test by using colored starch as a substrate. α-Amylase activities were detected at a level about 100-fold higher than the case for β-amylase. Glucoamylase and α- glucosidase could not react to the colored substrate. We could therefore reasonably evaluate the amount of each type of amylase activity in plants by comparing the value for the α-amylase unit (measured by the Phadebas test) with that for the β-amylase unit (measured by the G3-CNP method). We surveyed both types of amylase activity in several food materials to calculate the ratio of α-amylase/β-amylase, finding high β-amylase activity in the stem of the potato bean (Apios tuberose MOENCH).